In 1998 I did a survey for the Dutch AAA (ANWB) to see if members were willing to buy a Rocket eBook plus all ANWB travel guidebooks about France for $300. Response was very low by then (4% indicated they would probably buy, usually 35% meant 5% real sales).
Almost 10 years later there are still not many Travel Guide eBooks for sale. In Dutch there are only a few. Frommers has a pretty large selection and Rough guide has some city guidebooks. Lonely Planet has its Pick & Mix (chapters of some of their printed guidebooks, unfortunately only as PDF-files).